The present invention relates to distributorless ignition systems for internal combustion engines.
In an ignition system with non-rotary high-voltage spark distribution, usually called a distributorless ignition system, and one ignition coil per cylinder of the engine, it is usually necessary to provide two reference signals in order to unambiguously distinguish each of the cylinders. One of the reference signals is usually indicative of top dead center (TDC) of number 1 cylinder and is derived from the crankshaft. The other reference signal is required due to the fact that with a four stroke cycle, for each cylinder there are two TDC positions but only one spark is required. Consequently, a so-called "phase" signal is required which, when logically combined with the TDC reference signal, indicates the unambiguous position of the number 1 cylinder and hence each of the other cylinders. This "phase" signal is usually derived from the crankshaft every 720.degree. of crankshaft rotation.
It is absolutely necessary to check the phase signal at the start and during engine operation for logical correctness (for example phase signal present and not present in each case at successive reference marks, proper angular position with respect to reference mark) since an incorrect phase signal can lead to the drive to the ignition coils being offset by 360.degree. of crankshaft rotation and thus to an ignition of the mixture in the exhaust phase. Since this diagnosis of the phase transmitter requires monitoring of the reference mark transmitter and the phase transmitter over at least 360.degree. of crankshaft rotation even at the start of the engine before the first ignition is triggered, the starting times are significantly extended.
The present invention provides an ignition system for an internal combustion engine comprising means for generating a first signal indicative of a rotational position of the engine, means for generating a second signal indicative of a further rotational position of the engine, a plurality of ignition coils equal in number to or a multiple of, the number of cylinders in the engine, and computation means for computing and outputting ignition signals in response to the first signal. The ignition system according to the invention is characterized in that the computation means is arranged to address two cylinders of the engine at the same time, and to apply an ignition signal to a coil or coils associated with each of the two cylinders in the absence of a predetermined logical combination of the first and second signals.
This arrangement overcomes the disadvantage of extended starting times due to the fact that sparks are generated during the first revolution of the engine and until correct phasing of the ignition occurs. Should any fault occur in the means for detecting the second (phase) signal while the engine is running, it is possible to cause the processor to use the control method normally used for dual-spark coils as this will permit the engine to continue to operate although at some cost in terms of wear on the spark plug.
In order that the present invention be more readily understood an embodiment thereof will now be described by way of example with reference to the accompanying drawings, in which: